| Class | Number | Circum- tropical | Asiatic | American | Oceanic |
| Regular visitors | 17 | 2 | 13 | 1 | 1 |
| Uncommon visitors | 11 | 1 | 8 | 2 | 0 |
| Totals | 28 | 3 | 21 | 3 | 1 |
[A] Denotes birds which breed on both American and Asiatic sides of the Pacific Ocean.
The shore birds which are known to visit Micronesia breed in the Northern Hemisphere. [Table 3] summarizes the data concerning the breeding and wintering areas of these birds. As shown in part A of [table 3], 18 of the 28 species which visit Micronesia come from Asiatic breeding grounds. Seven have circumpolar breeding ranges and three (two are regular visitors) come from American breeding grounds. As shown in part B of table 3, 21 of the 28 waders have their winter ranges on the Asiatic side of the Pacific with eastern extensions to Micronesia and other parts of Oceania. Of the 7 remaining species, the winter ranges of three are circumtropical; the winter range of a fourth is restricted to Oceania; and the winter ranges of the remaining three (two classed as uncommon visitors) are American.
Bryan and Greenway (1944:109-115) record 14 species of shore birds from the Hawaiian Islands. One of these, Himantopus himantopus knudsoni, is a resident, probably of New World origin, according to Mayr (1943:56). The others, listed in [table 7], include three species unknown in Micronesia. One of these, Phalaropus fulicarus, apparently winters at sea off the west coast of South America. The other two species (Charadrius vociferus vociferus and Gallinago delicata) are classified by Bryan and Greenway as "accidental" and "occasional" visitors from North America. The ten species common to both the Hawaiian Islands and Micronesia include seven whose breeding grounds are circumpolar, two whose breeding grounds are in Arctic America and one whose breeding ground is in Arctic Asia. The winter ranges of these ten species include four which are circumtropical, three which are Asiatic, one which is restricted to Oceania, and only two which are American.
The ability of the shore birds to migrate almost as well over water as over land may explain their spread into Oceania. The likelihood that shore birds, when migrating may have ventured to Micronesia and Polynesia initially from the Asiatic side of the Pacific is strongly suggested by the data given in the paragraph above. Also, on the Asiatic side of the Pacific there are large numbers of islands, which form several archipelagoes extending from Kamchatka south to Malaysia. Once accustomed to migrating along these chains of islands from the Arctic to Australia, birds would probably have to make only minor adjustments to extend the breadth of their migratory routes eastward into the islands of the Pacific Ocean. In contrast, on the Pacific coast of North America there are few coastal or offshore islands and there is a vast area of open water separating the Hawaiian Islands from the American mainland. Probably the vastness of this area of water offers little stimulus to birds to expand their migratory ranges westward, and in part accounts for the small North American contingent in the population of shore birds of the Central Pacific. Some North American shore birds do visit the Pacific. The brisk trade winds from the northeast might be an aid to the birds in their flights from Nearctica to Hawaii.
The long flight now made by shore birds going from the Aleutians to the Hawaiian Islands may have commenced as a gradual expansion from the west, or perhaps such a route was initiated by birds flying northward through the Hawaiian Chain to the Arctic in migrating to their breeding grounds, and then later returning via the same route to reach their wintering grounds.
Routes of Migration
Fig. 6. Routes of migration used by shore birds in the Pacific area. From west to east these are: The Asiatic-Palauan Flyway, the Japanese-Marianan Flyway, the Nearctic-Hawaiian Flyway.